Heavy duty pneumatic radial tires with particular belt rubber configuration

ABSTRACT

A heavy duty pneumatic radial tire comprises a radial carcass and a belt superimposed about an outer periphery of the carcass and comprised of at least three rubberized cord layers, cords of two adjacent layers among these layers being crossed with each other at an acute cord angle with respect to an equatorial plane of the tire to form cross cord layers, in which a narrow-width cord layer among the cross cord layers is provided with an end cover rubber having a particular 100% modulus and a space cushion rubber having a particular 100% modulus.

This is a divisional of Application Ser. No. 09/066,998 filed Apr. 27,1998, now U.S. Pat. No. 6,016,859, which is a Divisional Application ofSer. No. 08/788,916, filed Jan. 22, 1997 now U.S. Pat. No. 5,779,828,the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heavy duty pneumatic radial tire, and moreparticularly to a heavy duty pneumatic radial tire for use in truck andbus in which cracks liable to be created at an end portion of a cordlayer in a belt and growth thereof are controlled and minimized tofavorably suppress the occurrence of separation failure due to the crackgrowth when the tire is applied to a heavy duty vehicle such as truckand bus.

2. Description of Related Art

It is well-known that as the running distance of the pneumatic radialtire mounted onto the heavy duty vehicle such as small-large size truckand bus increases, cracks are created at a cord end of a narrow-widthcord layer in cross cord layers having different widths, cords of whichlayers being crossed with each other at a relatively small cord anglewith respect to an equatorial plane of the tire, among plural cordlayers constituting the belt. The crack initially created is minute like“pecking” of the cord end, but such a minute crack propagates to a bigcrack along the cord as the running distance of the tire increases. Whenthe crack growth progresses in a certain extent, the front end of thecrack grows toward a cord end of the adjoining cord and finally cracksare connected to each other over substantially a full periphery of thecord layer along a side edge of the cord layer. If the crack growth isadvanced to this stage, a running time is not taken so much until theseparation failure is created between the cross cord layers.

Accordingly, a period ranging from the occurrence of minute crack at thecord end to the growth of connected crack along the side edge of thecord layer on its periphery controls a service life of the tire throughbelt separation failure. For this end, there are proposed variousimproving structures of the tire directed to the prolongation of tirerunning time (running distance) though the connection of cracks isunavoidable.

As the improving structure, JP-A-4-183605 proposes a heavy dutypneumatic radial tire wherein a cushion rubber is arranged between endportions of second and third cross steel cord layers counted from a sideof a carcass in a belt comprised of 3 to 4 steel cord layers and anupper side of an end portion of the third layer is covered with a rubberlayer having a thickness of not less than 1.5 mm to overlap over adistance of not less than 20 mm from the end of the layer and the rubberlayer is made from rubber having a JIS hardness of 65-75 and a modulusat 300% elongation of 130-200 kgf/cm².

Furthermore, JP-A-4-252705 discloses a heavy duty pneumatic radial tirewherein a belt edge cushion rubber is interposed between end portions oftwo cross steel cord layers in a belt comprised of four steel cordlayers and such end portion is covered with a rubber sheet having athickness of 1.0-3.0 mm and 50% modulus of the rubber sheet is smallerthan that of a coating rubber for the steel cord layer but larger thatthat of a base tread rubber. Moreover, JP-A-6-320906 proposes a heavyduty pneumatic radial tire wherein a belt comprised of four steel cordlayers is arranged between a base tread rubber of low modulus and acarcass and a cushion rubber is disposed between end portions of secondand third cross cord layers counted from a side of the carcass and theend portion is covered with a rubber sheet having a thickness of 0.8-3.3mm likewise the case of JP-A-4-252705 and further the rubber sheet has aJIS hardness lower than those of rubber for the second and third cordlayers and 50% modulus larger than that of the base tread rubber.

However, the effect of sufficiently controlling the crack growth undersevere service conditions of heavy loading, running speed and the likecan not be attained even by any improving structure of the beltdescribed in these prior proposals, so that belt separation failure isnaturally liable to be caused even in these new tires. Therefore, evenif the tire is recapped, it is obliged to prematurely create such afailure. Although this type of the heavy duty pneumatic radial tireparticularly tends to be important in the recapping adaptability, evenwhen the above new tire is completely run, the occurrence of the bigcrack unsuitable for the recapping is frequently observed at the endportion of the belt. Therefore, it is demanded to further improve thecrack resistance and resistance to crack growth at the end portion ofthe belt and hence considerably improve the resistance to beltseparation.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide a heavy dutypneumatic radial tire having an excellent long service life in which thecrack resistance and resistance to crack growth at the end portion ofthe cord layer constituting the belt, particularly narrow-width cordlayer in cross cord layers are sufficiently enhanced even under severerservice conditions of the tire while sufficiently maintaining therigidity-strengthening function inherent to the belt of the radial tireto thereby highly improve the resistance to separation in a new tire andalso improve the recapping adaptability.

According to a first aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and such anarrow-width cord layer is provided at its end portion with an end coverrubber covering the end portion and having a 100% modulus larger thanthat of a coating rubber for the narrow-width cord layer, and a spacecushion rubber having a 100% modulus smaller than that of a coatingrubber for each of the cross cord layers is disposed between the endportions of the cross cord layers so as to separate these end portionsfrom each other exceeding the thickness of the end cover rubber.

In the first aspect, the position relation of the cross cord layersamong the cord layers constituting the belt with respect to the radialcarcass is not particularly critical, but it is desirable that the crosscord layers are second and third layers or third and fourth layerscounted from a side of the radial carcass. Further, the end cover rubberindicates a sheet-shaped rubber covering each of the end portions of thenarrow-width cord layer from both surfaces thereof in the radialdirection of the tire otherwise specified. Also, the space cushionrubber is a rubber layer taperingly extending from an end of thenarrow-width cord layer or the end cover rubber toward inside andoutside of the tire. Moreover, the term “100% modulus” used herein meansa tensile stress at 100% elongation (kgf/cm²) measured according to atensile test method of a vulcanized rubber defined in JIS K-6251(1993).

In a preferable embodiment of the first aspect, the end cover rubber hasthe 100% modulus larger by at least 1.2 times than that of the coatingrubber for the narrow-width cord layer, and the space cushion rubber hasthe 100% modulus smaller by at least 0.95 times than that of the coatingrubber for the cross cord layers.

In another preferable embodiment of the first aspect, the 100% modulus(M₅) (kgf/cm²) of the space cushion rubber satisfies a relationship ofM₅≦M_(x)−(M₄−M_(x))×(G_(4E)/G_(5E)) with respect to 100% modulus (M₄)(kgf/cm²) of the end cover rubber, 100% modulus (M_(x)) (kgf/cm²) of thecoating rubber for the cross cord layers, gauge (G_(4E)) (mm) of the endcover rubber at the inside of the end of the narrow-width outer cordlayer in the radial direction of the tire and gauge (G_(5E)) (mm) of thespace cushion rubber existing on a vertical line drawn from an inner endof the narrow-width cord layer in the radial direction of the tire tothe inner cord layer of the cross cord layers.

In the other preferable embodiment of the first aspect, a width w (mm)of the end cover rubber at least located at the inside thereof in theradial direction of the tire satisfies a relationship of w≧(50 mm/N)×sinθ with respect to an inclination angle θ defined between a normal linedrawn from a corner of any cord end in the narrow-width cord layer atits developed plane view to a center axis line of a cord adjacentthereto and a straight line passing through cord ends of this layer andan end count N of the narrow-width cord layer per 50 mm as measured in adirection perpendicular to the cords of the layer, and an inner end ofthe end cover rubber having the width w in the widthwise direction ofthe belt is located in a region of arranging the space cushion rubber.

In a further preferable embodiment of the first aspect, the end coverrubber covers the surface of the end portion of the narrow-width cordlayer facing to the space cushion rubber and extends over this endportion toward the outside of the tire. This can be said to be simple ascompared with the end cover rubber defined in the aforementionedpreferable embodiments.

According to a second aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and such anarrow-width cord layer is provided at its end portion with a double endcover rubber covering the end portion and comprised of an outer rubberand an inner rubber having different compositions, and the outer rubberhas a 100% modulus larger than that of the inner rubber, and the innerrubber has a 100% modulus larger than that of a coating rubber for thenarrow-width cord layer.

This double end cover rubber is a sheet-shaped rubber covering each ofthe end, portions of the narrow-width cord layer from inside towardoutside in the radial direction of the tire likewise the first aspect ofthe invention otherwise specified.

According to a third aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and such anarrow-width cord layer is provided with an end cover rubber coveringeach of the end portions of this layer, and at least one of outerportion and inner portion of the end cover rubber in the radialdirection of the tire forms a wavy form in a direction perpendicular tothe cords arranged in the narrow-width cord layer, and a height betweena bottom and a peak of the wavy surface is within a range of 0.05-0.25mm.

In this case, the peak of the wavy form substantially corresponds withthe position of the central axis line of the cord embedded in thenarrow-width cord layer, while the bottom of the wavy form substantiallycorresponds with a central position between mutual adjoining cords.Moreover, an amplitude of the wavy surface in the end cover rubber ispreferable to be within a range of 0.07-0.20 mm.

According to a fourth aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and thecross cord layers are provided with a space cushion rubber separatingend portions of these layers and extending from an end of thenarrow-width cord layer toward the outside of the tire, and the spacecushion rubber is a rubber composite comprised of an inner rubberextending so as to separate the end portions of the layer from eachother and an outer rubber extending from the inner rubber toward theoutside of the tire and having at least two different rubbercompositions, and 100% moduli Mx′, M6 i and M6 u (kgf/cm²) of a coatingrubber for the narrow-width outer cord layer, inner rubber (6 i) andouter rubber (6 u) establish a relationship of M6 u<M6 i≦Mx′.

When the space cushion rubber is comprised of two rubbers, the positionof joint face between the inner rubber 6 i and the outer rubber 6 u maybe located on either an end of the narrow-width, cord layer or an end ofthe end cover rubber provided on the end portion of the layer as astandard point or may be within a region slightly separated from theabove standard point toward the inside or outside of the tire.

According to a fifth aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and such anarrow-width cord layer is provided with a space rubber covering anouter peripheral surface side of an end portion of the layer andprojecting outward from the end of the layer in the widthwise directionthereof, and an inner peripheral surface of the projected space rubberis located outward from an extrapolated extending surface of the outerperipheral surface of the narrow-width cord layer in the radialdirection of the tire, and the space rubber has a 100% modulus largerthan that of a coating rubber for the narrow-width cord layer.

If the end cover rubber is not provided on the end portion of thenarrow-width cord layer, the space rubber is arranged so as to directlycontact with the end portion, while if the end cover rubber is providedon the end portion of the layer, the space rubber is arranged so as todirectly contact with the outer periphery of the end cover rubber toseparate the end portion from a tread rubber. The space rubber is a flatsheet having a taper on its end portion and may be triangular ortrapezoidal in section, if necessary.

According to a sixth aspect of the invention, there is the provision ofa heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which thecross cord layers are provided with a side space rubber extendingbetween ends of these layers located at the same side, and the sidespace rubber has a 100% modulus smaller than that of a coating rubberfor the cross cord layers.

The side space rubber serves to separate the ends of the cross cordlayers from a tread rubber likewise the aforementioned space rubbercovering the outer peripheral surface side of the end portion of thenarrow-width cord layer. Therefore, it is required that an inner portionof the side space rubber in the radial direction of the tire covers theend of the inner cord layer among the cross cord layers, so that it isdesirable to arrange the side space rubber to extend over the end of theinner cord layer.

According to a seventh aspect of the invention, there is the provisionof a heavy duty pneumatic radial tire comprising a radial carcasstoroidally extending between a pair of bead cores embedded in a pair ofbead portions and a belt superimposed about an outer periphery of thecarcass to reinforce a tread portion and comprised of at least threerubberized cord layers, cords of two adjacent layers among these layersbeing crossed with each other at an acute cord angle with respect to anequatorial plane of the tire to form cross cord layers, in which anouter cord layer of the cross cord layers in a radial direction of thetire has a width narrower than that of an inner cord layer, and at leasta coating rubber for such a narrow-width cord layer among the cordlayers constituting the belt extends over an end of the cord in thislayer toward the outside of the tire, and a distance from the end of thecord to an outer end of the coating rubber is within a range of0.05-0.70 mm.

In general, cords in the cord layer constituting the belt slightlyprotrude from the coating rubber at an unvulcanized state and the cordlayer is built up into an unvulcanized tire at such a state, which isthen vulcanized to prepare a product tire in which the ends of the cordsare maintained at a state of slightly protruding from the coatingrubber. On the contrary, the tire of the seventh aspect is characterizedby surely and completely enveloping the cord end with the coating rubberas compared with the above conventional tire, which develops the effectof attaining the object of the invention. It is desirable that thedistance from the end of the cord to the outer end of the coating rubberis within a range of 0.10-0.50 mm.

The first to seventh aspects develop the effect of attaining the objectof the invention individually, but may be adequately and freely combinedin accordance with the severity of service conditions.

In order to favorably support the effect of attaining the object of theinvention, it is desirable that a belt under-cushion rubber is disposedbetween the carcass and an end portion of the cord layer located closeto the carcass and has a 100% modulus corresponding to 0.3-0.7 times the100% modulus of a coating rubber for this cord layer, or that eitherorganic fiber cord or steel cord is applied to the narrow-width cordlayer among the cross cord layers and the distance between the cords ina given end count is unequal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein:

FIG. 1 is a left-half section view of a main part of a first embodimentof the heavy duty pneumatic radial tire according to the inventions,

FIG. 2 is a partly enlarged view of the main part shown in FIG. 1;

FIG. 3 is a partly developed perspective view illustrating a group ofcords arranged in a narrow-width cord layer;

FIG. 4 is a left-half section view of a main part of a second embodimentof the heavy duty pneumatic radial tire according to the invention;

FIG. 5 is a left-half section view of a main part of a third embodimentof the heavy duty pneumatic radial tire according to the invention;

FIG. 6 is an enlargedly schematic section view in a directionperpendicular to cords arranged in an end portion of the narrow-widthcord layer;

FIG. 7 is a left-half section view of a main part of a fourth embodimentof the heavy duty pneumatic radial tire according to the invention;

FIG. 8 is a left-half section view of a main part of a fifth embodimentof the heavy duty pneumatic radial tire according to the invention;

FIG. 9 is a left-half section view of a main part of a sixth embodimentof the heavy duty pneumatic radial tire according to the invention

FIG. 10 is a left-half section view of a main part of a seventhembodiment of the heavy duty pneumatic radial tire according to theinvention;

FIG. 11 is a partly developed view illustrating a group of cordsarranged in another narrow-width cord layer;

FIG. 12 is a partly schematic section view perpendicular to a directionof arranging cords in the narrow-width cord layer;

FIGS. 13(a) and 13(b) are each a schematic view illustrating a shearingstrain acting to cord ends;

FIG. 14 is a graph showing a relation among crack length, rollingresistance and modulus ratio; and

FIG. 15 is a schematic view illustrating cracks created at a cord endportion of a narrow-width cord layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiments of FIGS. 1, 4, 5 and 7-10 showing left-half sectionsof their main parts with respect to an equatorial plane E of the tire, aradial carcass 1 toroidally extends between a pair of bead cores (notshown) embedded in a pair of bead portions (not shown) and is providedon its outer periphery with a belt 3 reinforcing a tread portion 2.Moreover, a tread rubber 2t shown in each of the above embodiments has atwo-layer structure of a cap rubber 2tc and a base rubber 2tb.

The belt 3 is comprised of at least three rubberized cord layers. In theillustrated embodiments, the belt 3 is comprised of four rubberized cordlayers 3-1, 3-2, 3-3 and 3-4 viewed from the side of the radial carcass1 in order. Among these cord layers 3-1 to 3-4, two adjoining cordlayers 3-2 and 3-3 form cross cord layers in which cords of the twolayers are crossed with each other at an acute angle of not more than90° defined between the cords of the layers with respect to theequatorial plane E of the tire. The cross cord angle is preferablywithin a range of 30-50° in order to satisfactorily develop the functionof the belt 3. In other words, it is desirable that the cords in each ofthe cross cord layers 3-2 and 3-3 are inclined at an angle of 15-25°with respect to the equatorial plane E. Although one set of the crosscord layers is existent in each of the above embodiments, the belt 3 mayinclude two or more sets of the cross cord layers.

As to the belt 3 having the above structure, the width of the cord layer3-3 located outward in the radial direction of the tire among the crosscord layers 3-2 and 3-3 is narrower than that of the cord layer 3-2, sothat ends of the cross cord layers 3-2 and 3-3 form a step difference assectionally shown in each drawing. Moreover, the width of each of thecord layers constituting the belt is substantially divided into equalparts with respect to the equatorial plane E.

The invention will be described below with reference to the embodimentsof FIGS. 1-4.

In FIGS. 1 and 2, the narrow-width cord layer 3-3 is provided with anend cover rubber 4 covering the end portion of the layer. The end coverrubber 4 shown in FIGS. 1 and 2 covers the end portion of the layer 3-3over a region ranging from an inner surface in the radial direction ofthe tire through the end to an outer surface thereof. On the other hand,the end cover rubber 4 shown in FIG. 4 covers only the inner surface ofthe end portion in the radial direction.

The end cover rubber 4 is necessary to have a 100% modulus M₄ (kgf/cm²)larger than a 100% modulus Mx′ of a coating rubber for the narrow-widthcord layer 3-3. Concretely, it is desirable that the 100% modulus M₄ iswithin a range of 1.2-4.0 times the 100% modulus Mx′ of the coatingrubber for the narrow-width cord layer.

In each of the above embodiments, the cross cord layers 3-2 and 3-3 areprovided with a space cushion rubber 5 separating end portions of theselayers from each other exceeding a thickness t of the end cover rubber4. The space cushion rubber 5 is necessary to have a 100% modulus M₅smaller than a 100% modulus Mx of a coating rubber for the cross cordlayers 3-2 and 3-3. Concretely, it is desirable that the 100% modulus M₅is within a range of not more than 0.95 times, preferably 0.5-0.9 timesthe 100% modulus Mx of the coating rubber for the cross cord layers 3-2and 3-3. Moreover, if the belt includes two or more sets of the crosscord layers, the end cover rubber 4 and the space cushion rubber 5 areapplied to a narrow-width cord layer having at least a maximum widthamong the narrow-width cord layers.

Referring to FIG. 2, it is advantageous that the 100% modulus M₅ of thespace cushion rubber 5 satisfies a relationship ofM₅≦Mx−(M₄−Mx)×(G_(4E)/G_(5E)) with respect to inner gauge G_(4E)of theend cover rubber 4 at the end of the narrow-width cord layer 3-3 in theradial direction, a gauge G_(5E)of the space cushion rubber 5 existingon a vertical line VL drawn from the end of the layer 3-3 to the innercord layer 3-2 in the cross cord layers, 100% modulus M₄ of the endcover rubber 4 and 100% modulus Mx of the coating rubber for the crosscord layers 3-2 and 3-3.

Referring to FIG. 3, both corners of each cord end C_(3E) in a group ofcords C₃ (only three cords show in FIG. 3) arranged in the narrow-widthcord layer 3-3 form an obtuse angle and an acute angle in its developedplane view, and each cord end C_(3E) substantially locates on a straightline EL. It is desirable that the width w of the end cover rubber 4satisfies a relationship of w≧(50 mm/N)×sin θ with respect to aninclination angle θ defined between a normal line HL drawn from any onecorner of a cord end C_(3E) of a certain cord C₃ to a center axis lineX₃ of another cord C₃ adjacent thereto and the straight line EL and anend count N of cords C₃ per 50 mm as measured in a direction of thenormal line HL. However, the end of the end cover rubber 4 having thewidth w inside the tire is terminated in a region of arranging the spacecushion rubber 5. Moreover, symbol Rc is a coating rubber for the cordC₃ in the narrow-width cord layer 3-3.

The invention will be described below with reference to the embodimentsof FIGS. 5 and 6.

In the embodiment of FIG. 5, the end portion of the narrow-width cordlayer 3-3 is covered with a double end cover rubber 14 comprised of aninner end cover rubber 14 i and an outer end cover rubber 14 o havingdifferent rubber compositions. In this case, the outer end cover rubber14 o has a 100% modulus M_(14o) larger than a 100% modulus M_(14i) ofthe inner end cover rubber 14 i. In fact, both moduli satisfyM_(14o)=(1.2-4.0)×M_(14i). Furthermore, the relationship of theaforementioned width w is applicable to a maximum width w_(max) of thedouble end cover rubber 14.

Although the space cushion rubber is not arranged in the embodiment ofFIG. 5, a stress-releasing rubber may be arranged likewise the case ofFIG. 1. Moreover, it is desirable that the 100% moduli M_(14i) andM_(14o) of the inner and outer end cover rubbers and 100% modulus Mx ofthe coating rubber for the cross cord layers 3-2 and 3-3 satisfy arelationship of (M_(14i)/Mx)=1.0-1.3 within a range of(M_(14o)/M_(14i))=1.2 4.0.

FIG. 6 enlargedly illustrates a section of the end portion of thenarrow-width cord layer 3-3 in a direction perpendicular to the cords C₃of this layer. As seen from FIG. 6, an end cover rubber 24 forms a waveat least at one of inner and outer sides in the radial direction (bothsides in the illustrated embodiment). A height H between bottom and peakof the wavy form is within a range of 0.05-0.25 mm, preferably 0.07-0.20mm. This peculiar wave can be formed by pressing a rubberized uncuredcord layer from both sides thereof by means of a comb roll similar to acomb roll for aligning many cords just before the coating with rubber inthe production of an uncured starting member for the narrow-width cordlayer through a calender roll, or by thinning a gauge of an uncuredcoating rubber as far as possible. In the latter method, however, thegauge of the coating rubber is too thin and hence the cord may beexposed from the coating rubber to cause an adhesion breakage in theexposed cord portion, so that the gauge of the coating rubber should berestricted to an extent that the cord is not exposed from the coatingrubber.

The invention will be described below with reference to the embodimentsof FIGS. 7-10.

A space cushion rubber 6 shown in FIG. 7 separates the end portions ofthe cross cord layers 3-2 and 3-3 from each other and extends from theend of the narrow-width cord layer 3-3 toward the outside of the tirelikewise the case of FIG. 1. However, the space cushion rubber 6 is arubber composite comprised of an inner rubber 6 i for separating the endportions of the cross cord layers 3-2 and 3-3 from each other and anouter rubber 6 u extending from the inner rubber 6 i toward the outsideof the tire and having at least two different rubber compositions, whichis entirely different from the case of FIG. 1.

Even when the end cover rubber is applied to the narrow-width cordlayer, the inner rubber 6 i and outer rubber 6 u always satisfy theabove position relation. When 100% moduli of the inner rubber 6 i andthe outer rubber 6 u are M6 i and M6 u, it is necessary that the 100%moduli M6 i and M6 u and 100% modulus Mx′ of the coating rubber for thenarrow-width cord layer 3-3 satisfy a relationship of M6 u<M6 i≦Mx′. Infact, it is preferable that (M6 u/M6 i) is within a range of 0.5-0.9 and(M6 i/Mx′) is within a range of 0.9-1.0. Moreover, a partition face Pbetween the inner rubber 6 i and the outer rubber 6 u may be inclinedinward or outward from the illustrated position.

In the embodiment of FIG. 8, the narrow-width cord layer 3-3 is providedwith a space rubber 7 covering the end portion of this layer from itsouter periphery side, which is arranged to project outward from the endof the narrow-width cord layer 3-3 in the widthwise direction of thebelt 3. In this case, however, the projected portion of the space rubberis located outward in the radial direction from an extrapolatedextending surface Ep of an outer surface of the narrow-width cord layer3-3 extended outward at a given curvature in the widthwise direction ofthe bell: 3.

Although the end cover rubber 4 and the space cushion rubber 5 arearranged together in the embodiment of FIG. 8, only the space rubber 7may be arranged to directly contact with the surface of the end portionof the narrow-width cord layer 3-3 without the arrangement of therubbers 4 and 5. Moreover, the space rubber 7 is required to have a 100%modulus M₇ larger than the 100% modulus Mx′ of the coating rubber forthe narrow-width cord layer 3-3. Concretely, it is desirable that the100% modulus M₇ is within a range of 1.2-4.0 times the 100% modulus Mx′.

In the embodiment of FIG. 9, the cross cord layers 3-2 and 3-3 areprovided with a side space rubber 8 extending between the ends of theselayers in addition to the end cover rubber 4 and the space cushionrubber 5. In the illustrated embodiment, the side space rubber 8 extendsinward over an end of the cord layer 3-2 in the radial direction of thetire. The side space rubber 8 has necessarily a 100% modulus M₈ smallerthan the 100% modulus Mx of the coating rubber for the cross cord layers3-2 and 3-3. Concretely, it is desirable that the 100% modulus M₈ iswithin a range of 0.5-0.9 times the 100% modulus Mx. Moreover, only theside space rubber 8 may be applied to the ends of the cross cord layers3-2 and 3-3 without the arrangement of the rubbers 4 and 5 likewise thecase of FIG. 8.

The embodiments of FIGS. 1-9 are effective to attain the object of theinvention individually or under a dependent relation thereto, but theymay be freely combined in accordance with the severity of serviceconditions. An example of such a combination is shown in FIG. 10. In thetire of FIG. 10, the end cover rubber 4 is provided on the narrow-widthcord layer 3-3, and the rubber composite comprised of the inner rubber 6i and the outer rubber 6 u is provided as the space cushion rubber 6arranged between the end portions of the cross cord layers 3-2 and 3-3,and the space rubber 7 is provided on the outer surface of the end coverrubber 4 in the radial direction, and the side space rubber 8 isarranged so as to extend between the ends of the cross cord layers 3-2and 3-3.

FIG. 11 is a partly developed view of an end portion of a narrow-widthcord layer 3-3 shown in accordance with FIG. 3, in which cord endsC_(3E) in a group of cords C₃ (shown by dotted lines) arranged in thelayer are existent substantially on a straight line EL and a coatingrubber Rc for the cord C3 extends over each cord end C_(3E) to an end3-3 e. It is required that a distance from the cord end C_(3E) to theend 3-3 e is within a range of 0.05-0.70 mm, desirably 0.10-0.50 mm. Inthis case, the application of the end cover rubbers 4, 14 and 24 is notalways required. If such rubbers are applied, it is desirable to apply arubber having the same rubber composition as the coating rubber for thenarrow-width cord layer in view of productivity instead of theaforementioned end cover rubbers 4, 14 and 24.

In the tires comprising the cross cord layers 3-2 and 3-3 in common withFIGS. 1-11, it is desirable that a belt under-cushion rubber 9 isarranged between the carcass 1 and the end portion of the cord layer 3-1in the belt 3 located nearest to the carcass 1. In this case, it isfavorable that a 100% modulus M₉ of the rubber 9 is within a range of0.3-0.7 times the 100% modulus Mx″ of a coating rubber for the cordlayer 3-1. Moreover, a mutual relation of 100% modulus in coatingrubbers for the cord layers 3-1 to 3-3 constituting the belt 3 may beMx″=Mx′=Mx or Mx″≈Mx′≈Mx.

Further, it is favorable to use steel cords or organic fiber cords suchas aramide fiber cords or the like as a cord in the narrow-width cordlayer. In this case, it is desirable that the cords C₃ are arranged atunequal distances as a section perpendicular to a direction of arrangingthe cords is shown in FIG. 12.

It is well-known that the growing rate of crack liable to be created atthe end portion of the narrow-width cord layer 3-3 in the cross cordlayers 3-2 and 3-3 is depended by two kinds of shearing strains producedthrough deformation at ground contact. Among these strains, a firststrain is a shearing strain γ_(st) acting between the cord and thecoating rubber along the direction of arranging the cords at a “pecking”stage created at the cord end. As a result, the crack grows in thecoating rubber surrounding the cord along the direction of arranging thecords.

A second strain is an interlaminar shearing strain γ₂₃ acting betweenthe end portion of the narrow-width cord layer 3-3 and the cord layer3-2 in the vicinity of the end C_(3E) of the cord C₃. The interlaminarshearing strain γ₂₃ mainly grows the crack along the cord to causeinterlaminar separation and then controls the growing rate of theinterlaminar separation. The behaviors of these shearing strains γ_(st)and γ₂₃ are illustrated in FIG. 13(a) and (b). FIG. 13(a) is aperspective view schematically showing only cords C₂, C₃ taken out fromthe end portions of the cross cord layers 3-2 and 3-3, while FIG. 13(b)is a plan view of cords C₂ and C₃.

As shown in FIG. 13(b), the shearing strain γ_(st) is dependent on thein-plane shearing strain LC of rubber located close to the end of thecord layer 3-3. In order to control the crack growth and prevent theoccurrence of separation failure, therefore, it is necessary tosimultaneously reduce the interlaminar shearing strain γ₂₃ and thein-plane shearing strain LC. Now, the reduction of both shearing strainsγ₂₃ and LC will be described below.

First, there are mentioned the following conclusions:

(1) If the 100% modulus M4 of the end cover rubber 4 is set to be largerthan 100% modulus Mx′ of the coating rubber for the cord layer 3-3, theshearing strain LC tends to decrease and the interlaminar shearingstrain γ₂₃ tends to increase;

(2) If the 100% modulus M₅ of the space cushion rubber 5 at leastlocated outward from the end of the cord layer 3-3 is set to be smallerthan the 100% modulus Mx′ of the coating rubber for the cord layer 3-3,both the shearing strain LC and interlaminar shearing strain γ₂₃ tend todecrease;

(3) If the 100% modulus M6 u of the outer rubber 6 u is set so as to besmaller than the 100% modulus Mx′ of the coating rubber for the cordlayer 3-3, the shearing strain LC decreases without increasing ordecreasing the interlaminar shearing strain γ₂₃;

(4) If the 100% modulus M₇ of the projected space rubber 7 is set to belarger than the 100% modulus Mx′ of the coating rubber for the cordlayer 3-3, the shearing strain LC decreases without increasing ordecreasing the interlaminar shearing strain γ₂₃;

(5) If the 100% modulus M₈ of the side space rubber 8 is set to besmaller than the 100% modulus Mx of the coating rubber for the crosscord layers 3-2 and 3-3, the shearing strain LC tends to decrease andthe interlaminar shearing strain γ₂₃ tends so as not to increase;

(6) If the 100% modulus Mg of the belt under-cushion rubber 9 is withina range of 0.3-0.7 times the 100% modulus Mx″ of the coating rubber forthe cord layer 3-1, both the shearing strain LC and the interlaminarshearing strain γ₂₃ tend to decrease.

The above items (1)-(6) develop the effect individually, but theincrease tendency of the interlaminar shearing strain γ₂₃ in the item(1) is undesirable, so that it is required to combine the item (1) withthe item (2). In such a combination, if the 100% modulus M₄ is not lessthan 1.2 ×Mx′ and the 100% modulus M₅ is not more than 0.95×Mx′, it ispossible to control the increase tendency of the interlaminar shearingstrain γ₂₃ and further control the shearing strain LC.

Further, the combination of the items (1) and (2) contributes to notonly the decrease of the shearing strain LC but also the effectivecontrol of the interlaminar shearing strain γ₂₃ if the 100% moduli M₄,M₅ and Mx and the gauge G_(4E)of the end cover rubber 4 and the gaugeG_(5E)of the space cushion rubber 5 are adequately set so as toestablish a relationship of M₅≦MX−(M₄−MX)×(G_(4E)/G_(5E)).

As to the decrease of the in-plane shearing strain LC in the above items(1)-(6), the following are mainly supplemented.

In items (1) and (4), the effect of controlling the in-plane deformationof rubber located close to the end of the cord layer 3-3 is obtained bycovering the end portion of the cord layer 3-3 with a high-modulusrubber or by covering the end portion from the outside in the radialdirection with such a rubber. The strain of rubber between the cordlayers 3-2 and 3-3 in item (2), the shearing strain LC and interlaminarshearing strain γ₂₃ are decreased by setting the 100% modulus M₅ of thespace cushion rubber 5 to a smaller value. Particularly, item (3)develops the effect of absorbing strain through displacement of stepportion of the cord layer 3-2 (step-difference portion to the cord layer3-3) because the 100% modulus M6 u of the outer rubber 6 u is lower thanthe 100% modulus Mx′ of the coating rubber for the cord layer 3-3. Initem (5), considering the distribution of the shearing strain LC ofrubber located close to the end of the cord layer 3-3, the 100% modulusM₈ of the side space rubber 8 is small, so that the shearing strain LCconcentrates in the side space rubber 8 and hence there is developed theeffect of mitigating the shearing strain LC of rubber located close tothe end of the cord layer 3-3.

In item (6), the 100% modulus M₉ of the belt under-cushion rubber 9 islarge, so that the rigidity between the carcass 1 and the cord layer 3-1increases and hence the tension-bearing of the cross cord layers 3-2 and3-3 is decreased by such an increment of the rigidity and the relativedisplacement of each cord layer in the circumferential direction underloading is reduced to decrease both the shearing strain LC and theinterlaminar shearing strain γ₂₃. The energy loss through the shearingstrain between the carcass 1 and the cord layer 3-1 increases, which cannot be ignored because the volume of the belt under-cushion rubber 9occupied is large. This is in a direction opposite to a recent demand ofmore reducing fuel consumption, so that it is favorable that the 100%modulus M9 is within a range of 0.3-0.7 times the 100% modulus Mx″ asshown in FIG. 14 in order to take a balance between strain and low fuelconsumption (low rolling resistance).

In FIG. 14, an abscissa is a value of modulus ratio M₉/Mx″, and a leftordinate is a value (index) of crack length K_(L), and a right ordinateis a value (index) of rolling resistance R.R. As seen from FIG. 14, thecrack length K_(L) and the rolling resistance R.R are in a conflictingrelationship.

As to the shearing strain γ₂₃, there will mainly be described thesignificance on the division of the space cushion rubber 6 deeplyparticipating in the shearing strain γ₂₃ into the outer rubber 6 u andthe inner rubber 6 i below.

When the end cover rubber 4 is applied at a larger value of 100% modulusM₄, even if interlaminar separation is created, the shearing strain γ₂₃in the end cover rubber 4 is smaller than the shearing strain γ₂₃ in thecoating rubber for the cord layer 3-3, so that the interlaminarseparation does never arrive at the space cushion rubber 5.

However, if it is required to reduce the number of constitutionalmembers, or if it is difficult to use an end cover rubber 4 having ahigher modulus in view of the productivity, there is adopted the spacecushion rubber 5. Even if the 100% modulus M₅ of the space cushionrubber 5 is a small value, the shearing strain γ₂₃″ in the space cushionrubber 5 becomes larger while the shearing strain γ₂₃ created in the endportion of the cord layer 3-3 is reduced. As a result, there is notparticularly caused a serious trouble while the crack at “pecking” stageprogresses in the coating rubber along the cord, but once such a crackgrows to the interlaminar separation, this separation rapidly grows inthe space cushion rubber 5 to cause trouble. Therefore, when the endcover rubber 4 having a large 100% modulus M₄ is not used, it isnecessary to take the following countermeasure after the occurrence ofthe interlaminar separation.

As a favorable countermeasure, the space cushion rubber 6 is dividedinto the outer rubber 6 u and the inner rubber 6 i so that the 100%moduli of these rubbers satisfy the relationship of M6 u<M6 i≦Mx′,whereby the 100% modulus of that portion of the space cushion rubber 6(inner rubber 6 i) arriving in the interlaminar separation is notlowered too much and the 100% modulus of the outer rubber 6 u is madesmaller than that of the inner rubber to decrease the in-plane shearingstrain LC and the shearing strain γ₂₃.

The control and reduction of the shearing strain γ₂₃ itself will bedescribed below.

Referring to FIG. 15 showing a group of cords C₃ as a developed viewsimilar to FIG. 3, cracks K created in the vicinity of each end C_(3E)of the cords C₃ through the action of the shearing strain γ_(st)frequently grow to a series of cracks K as the running of the tireproceeds. In this case, the position of the cracks K connecting betweenthe mutual adjoining cords C₃ tends to substantially match with a courseof arriving a normal line HL drawn from an obtuse corner of the endC_(3E) of the cord C₃ in the another adjoining cord C₃ even if the aboveposition is located close to the outside of the tire.

A distance w_(m) between the straight line EL and a straight line WL (ona developed view) connecting ends of the connected course of the cracksK between the mutual adjoining cords C₃ is a minimum width w of the endcover rubber 4, so that when the width w of the end cover rubber 4 isset to not less than (50 mm/N)×sin θ, the growing region of the crack Kbrought by the shearing strain γ_(st) is rendered into a reducing regionof the shearing strain γ_(st), whereby the growth of the crack K can becontrolled.

When the wave is formed on at least one side of the end cover rubber 24in the radial direction (see FIG. 6) (both sides in the illustratedembodiment), or when the end cover rubber 24 is fallen down between thecords C₃ to render the height H between bottom and peak of the wavysurface into a range of 0.05-0.25 mm, preferably 0.07-0.20 mm, theeffect of reducing the shearing strain γ_(st) can effectively bedeveloped.

Further, the coating rubber Rc for the cords C₃ arranged in thenarrow-width cord layer 3-3 is extend to an end 3-3 e over the cord endC_(3E) so as to render a distance y between the cord end C_(3E) and theend 3-3 e into a range of 0.05-0.70 mm, desirably 0.10-0.50 mm (see FIG.11) and the outer portion of the cord at its end C_(3E)in the radialdirection is covered with the coating rubber Rc having a relativelysmall value of 100% modulus, whereby the shearing strain γ_(st) can bereduced and hence it is possible to simply and effectively control thecrack K under a high productivity.

Finally, there is a relatively rare case that projection input isapplied to the belt 3 of the tire running on bad road. In this case, thecrack created at the end C_(3E) of the cord C₃ in the narrow-width cordlayer 3-3 shows a peculiar tendency of going away from the end C_(3E)rather than along the direction of arranging the cords C₃, which isentirely different from the aforementioned occurrence and growth of thecracks.

The application of the end cover rubber 4 having the 100% modulus M₄larger than 100% modulus Mx of the coating rubber Rc for thenarrow-width cord layer 3-3 is disadvantageous to such a peculiartendency. In this case, therefore, the double end cover rubber 14 isused in such a manner that the 100% modulus M_(14i) of the inner endcover rubber 14 i is made smaller than the 100% modulus M_(14o) of theouter end cover rubber 14 o, whereby the rubber having a large 100%modulus promoting the growth of cracks such as the end cover rubber 4 isseparated away from the end C_(3E) of the cord C₃ to control theoccurrence of cracks and at the same time delay the growing rate ofcracks and hence the occurrence of separation failure can be controlled.

In addition to the aforementioned effects, the distance between thecords C₃ embedded in the narrow-width cord layer 3-3 is made inequal asa whole, which contributes to reduce the shearing strain γ_(st),in-plane shearing strain LC and interlaminar shearing strain γ₂₃ andserves to delay a time of connecting cracks K (running time).

The following examples are given in illustration of the invention andare not intended as limitations thereof.

There are provided radial ply tires for truck and bus having a tire sizeof 10.00R20 and a structure as shown in FIGS. 1-12, in which the carcass1 is a single rubberized steel cord ply of radial arrangement, and thebelt 3 is comprised of four rubberized layers each containing steelcords of 3×0.20+6×0.36 structure. In the belt 3, a first cord layer 3-1has a width of 160 mm, a second cord layer 3-2 has a width of 185 mm,and a third cord layer 3-3 has a width of 160 mm, and a fourth cordlayer 3-4 has a width of 80 mm, while a cord inclination angle of eachcord layer with respect to the equatorial plane E of the tire is R52°,R18°, L18° and L18° in the order of the first to fourth layers (R meansupward to the right, and L means upward to the left). Therefore, thecross cord layers are the second and third cord layers.

The invention is also applicable to the third and fourth cord layers ina case that the cord inclining directions of the first to fourth cordlayers in the belt 3 are R, R, L and R in this order to form cross cordlayers between the second and third cord layers and between the thirdand fourth cord layers and the widths of the cord layer is made narrowerfrom the second cord layer to the fourth cord layer in order. Moreover,the cord inclining directions R, L may be replaced with each other.

The above tires having the common structure are divided into eightgroups of from Group 1 to Group 8. The dimension and test results everygroup are shown in the respective Table. Moreover, a belt under-cushionrubber 9 having 100% modulus M9 of 23 kgf/cm² is applied to theExamples, Comparative examples and Conventional Example in each group,respectively.

In Group 1, there are manufactured tires of Examples 1-12 according toFIGS. 1-3 and Example 13 according to FIG. 12 together with tires ofComparative Examples 1-7 and the conventional tire. In the tire ofExample 13, the cords of the cord layer 3-3 are divided into manybundles each containing three cords and the mutual bundles are separatedapart from each other.

In all of the Examples, Comparative examples and Conventional Example,rubber having the same rubber composition and 100% modulus Mx is used asa coating rubber for the cord layers 3-1 to 3-4 constituting the belt.In each tire, the end count N per 50 mm of the narrow-width cord layer3-3 is 24 cords and the inclination angle θ between the normal line HLof the cord C₃ and the straight line EL (see FIG. 3) is 72°, so that thevalue of (50 mm/N)×sin θ is 1.98. The values of 100% moduli, modulusration, gauges G_(4E)and G_(5E), w and Mx−(M₄−Mx)×(G_(4E)/G_(SE)) inthese examples are shown in Tables 1-3.

TABLE 1 Conventional Examples Items Example 1 2 3 4 5 6 100% Modulus(kgf/cm²) M_(x) 60 60 60 60 60 60 60 M₄ 60 72 80 90 100 80 80 M₅ 60 5050 50 50 56 53 Modulus ratio M₄/M_(x) 1.00 1.20 1.33 1.50 1.67 1.33 1.33M₅/M_(x) 1.00 0.83 0.83 0.83 0.83 0.93 0.88 Gauge G_(4E) (mm) 0.5 0.50.5 0.5 0.5 0.5 0.5 G_(5E) (mm) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 M₄ − (M₄ −M_(x)) (G_(4E)/G_(5E)) 60 58 56 54 52 56 56 Width of end cover 15 15 1515 15 15 15 rubber W (mm) Test results trouble form partial about aboutabout about about about separation on pecking pecking pecking peckingpecking pecking circumference crack length: 100 80 76 72 68 80 78(index)

TABLE 2 Conventional Examples Items Example 7 8 9 10 11 12 13 100%Modulus (kgf/cm²) M_(Y) 60 60 60 60 60 60 60 60 M₄ 60 80 80 80 80 80 8080 M₅ 60 56 56 56 56 56 56 56 Modulus ratio M₄/M_(Y) 1.00 1.33 1.33 1.331.33 1.33 1.33 1.33 M₅/M_(x) 1.00 0.93 0.93 0.93 0.93 0.93 0.93 0.93Gauge G_(4E) (mm) 0.5 0.3 0.5 0.5 0.5 0.5 0.5 0.5 G_(5E) (mm) 2.5 2.53.0 2.5 2.5 2.5 2.5 2.5 M₄ − (M₄ − M_(x)) (G_(4E)/G_(5E)) 60 58 57 56 5656 56 56 Width of end cover 15 15 15 2 5 10 20 15 rubber w (mm) Testresults trouble form partial about about about about about about aboutseparation on pecking pecking pecking pecking pecking pecking peckingcircumference crack length: 100 84 82 86 82 80 80 70 (index)

TABLE 3 Comparative Examples Items 1 2 3 4 5 6 7 100% Modulus (kgf/cm²)M_(x) 56 80 56 80 60 60 60 M₄ 80 60 60 56 56 68 80 M₅ 60 56 80 60 80 5056 Modulus ratio M₄/M_(x) 1.43 0.75 1.07 0.70 0.93 1.13 1.33 M₅/M_(x)1.07 0.70 1.43 0.75 1.33 0.83 0.93 Gauge G_(4E) (mm) 0.5 0.5 0.5 0.5 0.50.5 0.5 G_(5E) (mm) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 M₄ − (M₄ − M_(x))(G_(4E)/G_(5E)) 51 84 55 85 61 58 56 Width of end cover 15 15 15 15 1515 1 rubber w (mm) Test results Trouble form partial partial fullpartial full partial partial separation on separation on separation onseparation on separation on separation on separation circumferencecircumference circumference circumference circumference circumferencecircumference Crack length: 105 120 190 125 195 95 100 (index)

In Group 2, tires of Examples 14-16 are produced according to FIG. 4based on the tire of Example 5 together with tires of ComparativeExamples 8-12 and the conventional tire. In these tires, the end coverrubber 4 is arranged to cover the surface of the end portion at the oneside (inside in the radial direction) of the narrow-width cord layerfacing to the space cushion rubber 5 and extend over the end portionoutside the tire, and a rubber having the same rubber composition isused as the rubbers 4 and 5 and the coating rubber for the cord layers3-1 to 3-4 in the belt. The values of 100% moduli M₄, M₅ and Mx areshown in Table 4.

TABLE 4 Examples Comparative Examples Conventional Items 14 15 16 8 9 1011 12 Example 100% Modulus (kgf/cm²) M₄ 80 90 100 80 70 60 56 56 60 M₅56 56 56 60 80 56 80 60 60 M_(x) 60 60 60 56 56 80 60 80 60 Test resultsTrouble form about about about partial full partial full partial partialpecking pecking pecking separation on separation on separation onseparation on separation on separation on circumference circumferencecircumference circumference circumference circumference Crack length 8582 80 103 160 115 165 120 100 (index)

In Group 3, tires of Examples 17-20 are produced according to FIG. 5based on the tire of Example 4 together with tires of ComparativeExamples 13-17 and the conventional tire. The values of 100% modulus Mxof the coating rubber for the cord layers in the belt, 100% modulusM_(14i) of inner end cover rubber 14 i 100% modulus M_(14o) of outer endcover rubber 14 o in the double end cover rubber 14 are shown in Table5.

TABLE 5 Examples Comparative Examples Conventional Items 17 18 19 20 1314 15 16 17 Example 100% modulus (kgf/cm²) M_(14o) 100 115 130 100 10070 70 60 60 60 M_(14i) 70 70 70 60 60 100 60 100 70 60 M_(x) 60 60 60 6070 60 100 70 100 60 Test results Crack growing outward outward outwardoutward outward outward outward outward outward outward form from C_(3E)from C_(3E) from C_(3E) from C_(3E) from C_(3E) from C_(3E) from C_(3E)from C_(3E) from C_(3E) from C_(3E) Crack length 90 85 81 93 97 220 210240 230 100 (index)

In Group 4, tires of Examples 21-23 provided with the wavy end coverrubber 24 for the narrow-width cord layer 3-3 are produced according toFIG. 6 based on Example 5 together with tires of Comparative Examples18, 19 provided with the wavy end cover rubber having a height H betweenbottom and peak of wavy surface different from those of the examples.The height H (mm) of the wavy form in these tires is shown in Table 6.

TABLE 6 Comparative Examples Examples Items 21 22 23 18 19 Height ofwave 0.07 0.15 0.20 0.0 0.3 form H (mm) Test results Trouble form aboutabout about about about pecking pecking pecking pecking pecking Cracklength 92 85 89 100 96 (index)

In Group 5, tires of Examples 24-27 provided with the double cushionrubber 6 comprised of inner rubber 6 iand outer rubber 6 u are producedaccording to FIG. 7 based on the tire of Example 5 removing the endcover rubber together with tires of Comparative Examples 20-24 and theconventional tire. The values of 100% moduli M6 i, M_(6u) and Mx′ of theinner rubber 6 i, outer rubber 6 u and coating rubber for the cord layer3-3 are shown in Table 7.

TABLE 7 Examples Comparative Examples Conventional Items 24 25 26 27 2021 22 23 24 Example 100% Modulus (kgf/cm²) M_(6i) 60 60 60 56 56 45 6045 60 60 M_(6u) 54 45 36 45 60 60 56 56 45 60 M_(x) 60 60 60 60 45 56 4560 56 60 Test Results Trouble form about about about about full fullfull full partial partial pecking pecking pecking pecking separationseparation separation separation separation separation on circum- oncircum- on circum- on circum- on circum- on circum- ference ferenceference ference ference ference Crack length 93 85 80 84 190 185 195 165120 100 (index)

In Group 6, tires of Examples 28-31 provided with a projected spacerubber 7 are produced according to FIG. 8 based on the tire of Example 5together with a tire of Comparative Example 25 and the conventionaltire. The values of 100% moduli M₇, M₄, M₅ and Mx′ of the space rubber7, end cover rubber 4, space cushion rubber 5 and coating rubber for thecord layer 3-3 are shown in Table 8.

TABLE 8 Comparative Examples Example Conventional Items 28 29 30 31 25Example 100% modulus (kgf/cm²) M₇ 80 100 120 120 40 60 M₄ 60 60 60 80 6060 M₅ 60 60 60 56 60 60 M_(x)′ 60 60 60 60 60 60 Test results troubleform about about about about partial partial pecking pecking peckingpecking separation on separation on circumference circumference cracklength: 94 92 90 74 103 100 (index)

In Group 7, tires of Examples 32-35 provided with the side space rubber8 are produced according to FIG. 9 based on the tire of Example 5together with a tire of Comparative Example 26 and the conventionaltire. The values of 100% moduli M₈, M₄, M₅ and Mx of the space rubber 8,end cover rubber 4, space cushion rubber 5 and coating rubber for thecross cord layers 3-2, 3-3 are shown in Table 9.

TABLE 9 Comparative Examples Example Conventional Items 32 33 34 35 26Example 100% modulus (kgf/cm²) M₈ 54 45 36 45 70 60 M₄ 60 60 60 80 60 60M₅ 60 60 60 56 60 60 M_(x) 60 60 60 60 60 60 Test results trouble formabout about about about partial partial pecking pecking pecking peckingseparation on separation on circumference circumference crack length: 9492 90 76 104 100 (index)

In Group 8, tires of Examples 36-38 applying a wide-width coating rubberRc to the narrow-width cord layer 3-3 are produced according to FIG. 11based on the tire of Example 5 together with tires of ComparativeExamples 27, 28. The distance y (mm) between the cord end C_(3E) in thenarrow-width cord layer 3-3 and the end 3-3 e of the coating rubber Rcis shown in Table 10.

TABLE 10 Comparative Examples Examples Items 36 37 38 27 28 Distance y(mm) 0.1 0.3 0.5 0.0 1.0 Test results trouble form about about aboutabout about pecking pecking pecking pecking pecking crack length: 85 7273 100 95 (index)

Each tire in Examples 1-16 and 21-38, Comparative Examples 1-12 and18-28 and Conventional Examples of Groups 1, 2 and 4-8 other than Group3 is pushed on a drum of a testing machine under conditions of internalpressure: 7.00 kgf/cm² and load: 2600 kgf and run at a speed of 60 km/hover a distance of 100,000 km and thereafter taken out from the testingmachine. Then, the tire is cut to measure a crack length grown the mostamong cracks created at the end portion of the belt 3. Such a crack iscreated in the end portion of the third cord layer in all tires. Thecrack length is an average of values measured on 30 positions atsubstantially an equal interval in the circumference of the tire andrepresented by an index on the basis that the conventional example orcomparative example is 100. The smaller the index value, the better theproperty of controlling the occurrence of cracks. The test results arealso shown in Tables 1-4 and 6-10 as a form of trouble, and a cracklength (index).

In the term “Trouble form”, the separation means interlaminar separationbetween the narrow-width cord layer 3-3 and the cord layer 3-2, and thewording “partially separation on circumference or partial separation”means that the separation is partially created along the circumference,and the wording “about pecking” means that the trouble at the end of thenarrow-width cord layer is controlled to a pecking degree.

Each tire in Examples 17-20, Comparative Examples 13-17 and theconventional example in Group 3 is pushed on a drum of a testing machineprovided on its circumference with 6 semi-spherical projections having aradius of 30 mm to strike each projection onto the end portion of thenarrow-width cord layer 3-3 under conditions of internal pressure: 7.00kgf/cm² and load: 2600 kgf and then run at a speed of 60 km/h over adistance of 100,000 km. The evaluation is carried out in the same manneras described above to obtain test results as shown in Table 5. In thiscase, however, the trouble form is expressed as a crack growing form forincluding the growing direction of the crack, in which the wording“outward from C_(3E)” means a state of growing the crack slantly fromthe cord end C_(3E) toward the outside of the tire without growing alongthe cord C₃. This test of riding over the projection is high in thereliability as an alternative test for running on bad road.

As seen from tables 1-10, the tires of Examples 1-38 do not show theoccurrence of partial separation and largely decrease the crack length,so that they are considerably superior to the tires of the comparativeexamples and conventional examples in the resistance to crack growth andthe separation resistance. This is true to prove that the first toseventh aspects of the invention are considerably effective to controlthe growth of cracks individually or in combination thereof.

As mentioned above, according to the invention, the occurrence andgrowth of cracks liable to be created at the end portions of the crosscord layers are advantageously controlled by rationalizing distributionof 100% moduli between coating rubbers for the cross cord layers in thebelt and rubber neighborhood to the end portion of these layers orfurther by arranging a new rubber member on the end portions of thecross cord layers and slightly widening the width of the coating rubberfor the narrow-width cord layer without causing any inconvenience in thestructure of the belt itself, whereby it is possible to largely improvethe separation resistance of the belt. As a result, the invention canprovide heavy duty pneumatic radial tires capable of not only assuring along service life in a new product but also sufficiently coping withrepetitive recapping.

What is claimed is:
 1. A heavy duty pneumatic radial tire comprising aradial carcass toroidally extending between a pair of bead coresembedded in a pair of bead portions and a belt superimposed about anouter periphery of the carcass to reinforce a tread portion andcomprised of at least three rubberized cord layers, cords of twoadjacent layers among these layers being crossed with each other at anacute cord angle with respect to an equatorial plane of the tire to formcross cord layers, in which an outer cord layer of the cross cord layersin a radial direction of the tire has a width narrower than that of aninner cord layer, and such a narrow-width cord layer is provided with anend cover rubber covering each of the end portions of this layer, and atleast one of an outer portion and an inner portion of the end coverrubber in the radial direction of the tire forms a wavy form in adirection perpendicular to the cords arranged in the narrow-width cordlayer, and a height between a bottom and a peak of the wavy surface iswithin a range of 0.05-0.25 mm.